Variable oil-gas fuel control system



\ P. M. DANA Filed Jan. 25. 1951 VARIABLE OIL-GAS FUEL CONTROL SYSTEM Aug. 11, 1953 Patented Aug. 11, 1953 VARIABLE OIL-GAS FUEL CONTROL SYSTEM Paul M. Dana, Billings, Mont., assignor to Standard Oil Development Company, a corporation of Delaware Application January 25, 1951, Serial No. 207,709 2 Claims. (Cl. 236-26) The present invention is concerned with an improved apparatus for controlling the amount of liquid fuel and gaseous fuel supplied to burner elements. The invention is particularly concerned with a variable oil-gas combustion fuel control system. The variable oil-gas combustion fuel control of the present invention is designed to give a much improved method of firing a maximum available amount of gas together with a minimum amount of fuel oil to produce an equivalent B. t. u. basis. The invention comprises an improved system of splitting control air loading and utilizes proportional band and control point of proportional pressure controller to establish the gas pressure operating range and bandwidth.

It is Well known in the art to employ gaseous and liquid fuels in a furnace system. For instance, in the refining of petroleum oils, byproducts of the rening operation comprises reiinery gases, which gases are utilized in the burners of various furnaces. In these operations the amount of gas available is not suiflcient and it is desired to provide a continuous method of supplementing the gaseous fuel with a liquid fuel. Many proposals have been made directed toward manual operation which in many instances was not entirely satisfactory. In accordance with the present method, an apparatus is provided which will control the amount of liquid fuel utilized in a burner depending upon the amount of gaseous fuel available in order to provide a predetermined amount of B. t. u.s available at the burner.

The present invention may be readily understood by reference to the drawing illustrating the same wherein the single ligure is a diagrammatic View of the control system. The drawing illustrates the use of a splitter beam for supplying a required B. t. u. input to a burner when utilizing a gaseous and liquid fuel. A novel arrangement of air-operated valves and diaphragm valves are employed to eiiiciently and effectively secure this result. Referring specifically to the drawing, an air supply under suilicient pressure is introduced into a master air controller` I by means of line I. The pressure of this air may vary appreciably, as for example in the range from l0 to 25 lbs. per sq. in. but for the purpose of description, is assumed to be about 17 lbs. per sq. in. For. purpose of illustration, the invention will be described with respect'to a steam boiler, thus, as the B. t. u. content of the burner system goes lower, the pressure in the boiler will drop, thus indicating that additional fuel should be supplied to the burner. Conversely, if the pressure increases, the control is such that less B. t. u.s will be supplied to the burner. Thus, the steam pressure on the boiler is transmitted to the master air controller I0 by means of line 2. Thus, primary air control loading is from the master air controller IIJ which puts out .a loading in line 3 (air pressure) proportional to the change in primary load as exerted through line 2. Under these conditions, the air loading will go unrestricted through initial conduit means or line 3 to initial diaphragm A. 'I'he load will .also pass through diaphragm operated ratio valve 4 to secondary diaphragm B. The air load will also pass unrestricted to spring closing fuel oil control valve 5.

Thus, when no fuel gas is available, the amount of oil supplied to the burners by means of line 6 is directly controlled by fuel oil control valve 5 which adjusts the amount of oil passed into line 6 from line 1. Fuel oil control valve 5 in turn is controlled by the air load from the master air controller' I0 which in turn is a function of the load requirement exerted through line 2. Under these conditions, the air loading on initial diaphragm A will be equal to the air loading on secondary diaphragm B and the force on splitter beam 8 will be in balance with no air loading on tertiary diaphragm C, which is exerted by means of line 9.

As the fuel gas quantity builds up the pressure in fuel gas, line II will increase. The amount of fuel gas supplied to the burners by means of line I2 is controlled by a spring closing gas control feed valve I3 which in turn is controlled as hereinafter described.

As the gas supply increases the pressure in line I I increases to a predetermined amount, this pressure is transmitted to gas pressure controller 20 by a secondary conduit means I4. A supply air under sufficient pressure is introduced into gas pressure controller 20 by means of line I5. As the fuel gas pressure increases to a predetermined point on unit 20, the supply air is cau-sed to operate diaphragm operated ratio valve 4 by means of line I 6. In operation, valve 4 functions to reduce some of the air pressure of the initial conduit means. Under these conditions the pressure on valve 5 decreases due to reduction in pressure through ratio valve 4, thus causing the valve to atleast partially close. Furthermore, the pressure on secondary diaphragm B decreases, while the pressure on initial diaphragm A remains substantially constant. Thus, the force on splitter beam 8 with respect to valves A and B becomes unbalanced thereby forcing the beam downwardly in a manner to parti-ally close the port of nozzle I1. Nozzle I1 is continually supplied with air by means of line I8 at a constant pressure. Under these conditions, pressure builds up in line 9 and is transmitted to the diaphragm of pressure balance gas control valve I3 in a manner to partially open the same, thus, supplying the fuel gas from line II to line I2 for transmittal to the burner.

Pressure also builds up on tertiary diaphragm C, which pressure in turn is transmitted to splitter beam 8 to supplement the force supplied by diaphragm B. Thus, the force exerted by diaphragm valves B and C is balanced with respect to the splitter beam with the force exerted by diaphragm valve A. If suicient fuel gas is available, sufficient reduction in pressure occurs through valve 4 so that the fuel oil valve 5 is closed and no pressure is exerted by secondary diaphragm B. Diaphragms A and C are in balance and pressure balance gas control valve I3 is open supplying the necessary fuel to give the required B. t. u.s.

The present invention is concerned with an apparatus for securing an improvement in the method of firing more than one fuel to a steam boiler or other combustion heater. The primary purpose is to utilize waste fuel gas to the maximum extent available and supplement fuel oil to supply the demand. The invention comprises a particularly novel arrangement of known equipment components. The equipment comprises a proportional band recording pressure controller with the control set point and dial type proportional band set. Pressure element 20 is sized to cover the pressure range of waste fuel gas. The gas pressure controller 2U comprises a unit similar or equivalent to the one described in the Foxboro Book M-40, Proportional Band Pressure Controller on page l of their catalog 11-358 published February 1947 by the Foxboro Manufacturing Company of Foxboro, Mass. The force balance pressure splitter is designed to balance a diaphragm loading on one side of a fulcrum against two diaphragm loadingson the opposite side in such a manner that the sum of the output air loading from the two band diaphragms is equal in pressure to the left hand side. The master air controller comprises one complete with throttling band and reset which will put out an Iair loading proportional to theprocess demand-in the instances described, a pressure controller to maintain constant steam boiler pressure. l

The diaphragm operated ratio valve 4 is designed in such a manner that it will take any given air loading input, as for example from 3 to l5 lbs. per sq. in. and give a decreased air pressure output proportional to diaphragm loading from gas pressure controller 20.

The fuel oil control valve 5 comprises a diaphragm operated fuel oil control valve sized Ato pass the maximum amount of fuel oil demanded by the process. The pressure balance gas control valve I3 comprises a fuel gas diaphragm operated control. valve, sized to pass the maximum amount of fuel gas demanded by the process.

As pointed out, primary control air loading is from the master controller II) which puts out a loading proportional to the change in primary load line 2 when no waste fuel gas is available. This air loading will go unrestricted through line 3 to diaphragm A, through open ratio valve 4 to diaphragm B and fuel oil control valve 5, thereby controlling the load 100% on fuel oil. Air

4 loading on diaphragm A will be equal to air loading on diaphragm B, and the force balance splitter beam I9 will be in balance with no air loading on diaphragm C, line 9 or control valve I3. As the waste gas pressure increases, pressure controller 20 receiving a pressure change through line I4 will put out a control air loading through line I6 proportional to the control point setting and throttling band setting of the instrument. This loading on the diaphragm of ratio valve 4 will cause the ratio valve to reduce the pressure of the control air in line 2 I. This will cause valve 5 to start closing and at the same time put an unbalance in loading between diaphragms A and B. This unbalance will force the splitter beam I9 down toward the air nozzle causing a buildup in air pressure in line 9 to control valve I3 and diaphragm C. Valve I3 will start opening, admitting waste fuel gas to the firebox of the unit being controlled. This air loading will increase until the sum of the air loadings on diaphragms B and C is equal to the loading on diaphragm A. The splitter beam will then come into balance and. the load will be partially carried by fuel oil and partly carried by waste gas.

As the quantity of waste fuel gas increases, the increase in control air loading from controller 20 will gradually close ratio valve 4 until at maximum gas availability, there will be no air loading on line ZI, valve 5 or diaphragm B. Air loading from controller I0 will then be going only to diaphragm A; the splitter balance will be between diaphragm A and diaphragm C, and the loading to valve I3 will be exactly equal to that coming from controller I0. The unit will then be on waste gas firing. It should be noted that a change in controlled air from controller I0 will change the air loading to both valves 5 and I3 but that the sum of these two air loadings will always equal exactly the air loading from controller I0. This relationship will hold precisely over the full control range of controller I0. By maintaining a constant fuel oil pressure to valve 5 and using a pressure balanced diaphragm on valve I3, the B. t. u. input to the iirebox will remain relatively constant for a constant load requirement regardless of control shift from one oil-gas ratio to another. Minor variations in B. t. u. input will be smoothly and rapidly taken care of by the reset element of controller I0.

The point at which fuel gas is first fired and the point at which the rlrebox is 100% on fuel gas are controlled by pressure controller 20. As an example, it is assumed that it is desirable to admit waste fuel gas When its pressure builds to 32 p. s. i. and that the unit will be 100% on waste fuel gas when gas pressure reaches 42 p. s. '1. With a 50 p. s. i. pressure element in pressure controller 20, the 10 p. s. i. maximum-minimum range would be equivalent to a 20% throttling range. Setting the control point to 37 p. s. i. and the throttling band to 20, controller 20 would start to put out an air loading at 32 p. s. i. and would be putting out a maximum air loading at 42 p. s. i.

The width of the pressure control range may be set at any desired value and the maximumminimum may be shifted up and down the pressure band in a linear manner. For instance, the control pressure Width could be shifted from 32 p. s. i.42 p. s. i.to 22 p. s. i.-52 p. s. i. simply by moving the throttling band to a setting of 30. Likewise, the 32 p. s. i.42 p. s. i. control range could be shifted to 40 p. s. i.-50 p. s. i. by moving the control `point to 45 p. s. i. In accordance with the present invention, the oil-gas fuel control will re any combination of oil and gas to a flrebox utilizing all waste gas available in a superior manner.

Having described the invention, it is claimed:

1. Apparatus for controlling the relative ratio of fuel-oil and fuel-gas to a burner in order to maintain a predetermined B. t. u. input which comprises a master air controller actuated as a function of boiler pressure and which controls a varying air pressure as a function thereof, a fuel oil control valve positioned between an oil supply line and the burner and controlled by the varying of air pressure exerted thereon, an initial conduit means connecting said master air controller and said fuel oil control valve whereby the air pressure varied by said master air controller is exerted on said fuel oil control valve, a dia- .phragm operated ratio valve positioned in said initial conduit means adapted to reduce the pressure in said initial conduit means adjacent said fuel oil control valve as air pressure is exerted on said diaphragm, a pressure balance gas control valve positioned between a fuel gas supply line and the burner and controlled by the varying of air pressure exerted thereon, a secondary conduit means connecting said fuel gas supply line and a Waste gas controller actuated as the pressure of the gas in said secondary conduit means varies, and which controls a varying air pressure as a function thereof in a manner to operate said diaphragm operated ratio valve, an initial diaphragm positioned by means of a conduit off said initial conduit means between said master air controller and said diaphragm operated ratio valve, a secondary diaphragm positioned by means of a conduit off said initial conduit means between said diaphragm operated ratio valve and said fuel oil control valve, said initial and said secondary diaphragm valves being actuated by the air pressure in said initial conduit means, whereby as said diaphragm operated ratio valve reduces pressure, the pressure on said secondary diaphragm is reduced, a balance beam actuated on opposite sides by said initial and secondary diaphragms, whereby said balance beam is in balance when the air pressure in said diaphragme is equal, an air nozzle positioned with respect to said balance beam in a manner that as the pressure on said initial diaphragm exceeds the pressure on said secondary diaphragm said balance beam will function to gradually close said air nozzle, a tertiary conduit means connecting said air nozzle and said pressure balance gas control valve, said tertiary conduit means also connecting said nozzle and a tertiary diaphragm, said tertiary diaphragm being positioned in a manner to exert a supplementary force with respect to said secondary diaphragm valve on said balance beam, whereby as the pressure in said tertiary conduit means increases due to said balance beam restricting said air nozzle, said pressure balance control valve will open and said tertiary diaphragm will supplement the force exerted by said secondary diaphragm in a manner to counteract the force exerted by said initial diaphragm and bring said balance beam into equilibrium.

2. Apparatus as dened by claim 1 wherein said burner comprises fuel oil ports and fuel gas ports.

PAUL M. DANA.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,781,174 Greenfield Nov. 11, 1930 2,134,745 Ziebolz et al Nov. 1, 1938 2,394,297 Fayles Feb. 5, 1946 2,507,119 Randall et al May 9, 1950 

